1. Field of the Invention
The present invention relates to hazardous material sensors and, more particularly, to a method and apparatus for extracting information from an array of hazardous material sensors.
2. Description of the Related Art
Hazardous materials may be used in many ways to threaten the health and/or welfare of a civilian population. For example, a nuclear or biological device may be brought to a population center and detonated thereby causing catastrophic loss in terms of life and assets. To detect the presence of nuclear and/or biological materials, it is possible to deploy sensors designed to detect the presence of such materials. The sensors may be mobile and transported around and between cities to search for pockets of increased readings characteristic of the presence of the hazardous material. Alternatively, the sensors may be deployed in an array within a population center such as a city or town to sense if hazardous materials are being transported in and through the population center.
Existing hazardous material sensors are able to detect many different types of hazardous materials. Generally, to increase sensitivity, the sensors are required to be increased in size. For example, a radiation sensor has a sensitivity roughly proportional to its volume, and must be very large to sense a dirty bomb at 30 feet. In addition, sensors exhibiting higher sensitivity to the particular hazardous material of interest generally are more costly. The combination of the increased size and increased cost makes high sensitivity sensors more difficult to deploy discretely and ubiquitously in a population center.
Accordingly, it would be better from a cost and deployment perspective if the sensors to be deployed were able to be made relatively small and inexpensive. Unfortunately, due to the relatively high background noise level and the concomitant low signal to noise ratio experienced by many small low cost sensors, small sensors generally are considered unsuitable for use in hazardous material sensing networks.
One known way of extracting statistically significant data from an array of low gain sensors is through the use of correlation. Specifically, as an object moves through a linear array of sensors, readings may be taken from the sensors when the object is in close proximity to the sensor. By aggregating the readings from all the sensors it is possible to reduce the noise level to enable the signal to emerge and, hence, to discern the presence of hazardous material on the object that is passing through the sensor array, even where any one of the individual sensors would not be able to detect the hazardous material on its own.
While correlation works well when an object travels along a known trajectory past a set of sensors at predictable times, persons carrying hazardous materials in a population center may be expected to travel erratically and, hence, not pass the sensors in the population center at predictable times or in a predictable order. Accordingly, it would be advantageous to provide a new way of extracting information from an array of hazardous material sensors deployed, for example, in a population center.